Passive cooling articles having a fluoropolymer

Abstract

A passive cooling article is disposed on a substrate to cool the substrate. The article includes an outer layer having a high absorbance in the atmospheric window region of the electromagnetic spectrum and having a high transmittance in the solar region of the spectrum. The article also includes a reflector having a high reflectivity in the solar region of the spectrum. At least one of the outer layer and the reflector includes a fluoropolymer. Micro-sized particles or surface structures may be disposed in or on the outer layer or the reflector to improve absorbance. A metallic layer may be disposed between the fluoropolymer and the substrate to be cooled.

1 . A passive cooling article comprising:
 a reflector having an average reflectance of at least 85% in a first wavelength range from 0.35 to 2.5 micrometers and comprising at least one optical layer; and   an outer layer at least partially covering the reflector and having an absorbance of at least 0.15 in a second wavelength range from 8 to 13 micrometers, wherein the outer layer comprises a fluoropolymer.   
     
     
         2 . A passive cooling article comprising:
 a reflector having an average reflectance of at least 85% in a first wavelength range from 0.35 to 2.5 micrometers, the reflector comprising a plurality of first optical layers and a plurality of second optical layers, wherein each of the first optical layers comprises a fluoropolymer; and   an outer layer at least partially covering the reflector and comprising an array of inorganic particles effective D 90  particle size of at most 40 micrometers.   
     
     
         3 . A passive cooling article comprising:
 a reflector having an average reflectance of at least 85% in a first wavelength range from 0.35 to 2.5 micrometers, the reflector comprising a plurality of first optical layers and a plurality of second optical layers, wherein each of the first optical layers comprises a fluoropolymer; and   an outer layer at least partially covering the reflector and comprising an array of surface structures formed on a surface of the outer layer, each surface structure having an average width up to 40 micrometers.   
     
     
         4 . The article of  claim 2 , wherein the outer layer comprises a fluoropolymer. 
     
     
         5 . The article of  claim 2 , wherein the average reflectance of the reflector is at least 90% in the first wavelength range. 
     
     
         6 . The article of  claim 2 , wherein the absorbance of the article is at least 0.8 in the second wavelength range. 
     
     
         7 . The article of  claim 2 , wherein the fluoropolymer comprises at least one of:
 a polymer of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride,   a polymer of tetrafluoroethylene, hexafluoropropylene, vinylidene fluoride, and perfluoropropyl vinyl ether,   a polyvinylidene fluoride,   an ethylene chlorotrifluoroethylene polymer,   an ethylene tetrafluoroethylene polymer,   a perfluoroalkoxy alkane polymer,   a fluorinated ethylene propylene polymer,   a polytetrafluoroethylene, or   a polymer of tetrafluoroethylene, hexafluoropropylene, and ethylene.   
     
     
         8 . The article of  claim 1 , wherein the reflector comprises a multi-layer optical film comprising a plurality of first optical layers and a plurality of second optical layers, wherein each first optical layer comprises a fluoropolymer. 
     
     
         9 . The article of  claim 2 , wherein a first refractive index of the plurality of first optical layers is less than a second refractive index of the plurality of second optical layers by at least 5%. 
     
     
         10 . The article of  claim 2 , wherein the plurality of first optical layers comprises a polymer of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride. 
     
     
         11 . The article of  claim 10 , wherein the plurality of second optical layers comprises polyethylene terephthalate. 
     
     
         12 . The article of  claim 1 , further comprising an array of inorganic particles at least one of dispersed in or disposed on at least one of the outer layer or the reflector and having an effective D 90  particle size of at most 40 micrometers. 
     
     
         13 . The article of  claim 2 , wherein the beads comprise a ceramic material. 
     
     
         14 . The article of  claim 2 , wherein the reflector comprises a metallic layer comprising at least one metal, the metallic layer having an average reflectance of at least 90% in a fourth wavelength range from 1.2 to 2 micrometers. 
     
     
         15 . The article of  claim 2 , further comprising an array of surface structures formed on a surface of the outer layer and having an average width of at most 40 micrometers. 
     
     
         16 . The article of  claim 3 , wherein each surface structure is at least one of integrated into or on the outer layer. 
     
     
         17 . The article of  claim 2 , wherein the reflector has a maximum thickness of at most 40 micrometers. 
     
     
         18 . The article of  claim 2 , wherein the fluoropolymer-containing layer has an absorbance of less than 1 in a third wavelength range, wherein the third wavelength range is contained in the second wavelength range and has a frequency bandwidth of at least 10 micrometers, and at least one different layer in the article have an absorbance of at least 1 in the third wavelength range. 
     
     
         19 . An apparatus comprising:
 a substrate capable of being cooled comprising at least a portion of a surface configured to be exposed to solar energy; and   the article of  claim 2  covering at least the portion of the surface of the substrate to reflect solar energy directed toward the surface.   
     
     
         20 . The apparatus of  claim 19 , wherein the substrate is coupled to a heat transfer system.